The present embodiments relate to segmenting a two-dimensional angiographic recording of a vessel of a body.
One established clinical characteristic is the fractional flow reserve (FFR), which may be measured with a compression wire, for example. In such cases, the compression wire is guided past a stenosis in the vessel or vascular segment of the body, and the pressure is determined there distally in relation to the stenosis. This distal pressure is divided by the proximal pressure in order to calculate the fractional flow reserve.
It is possible to calculate the pressure course across the stenosis using mathematical fluid dynamics methods (e.g., computational fluid dynamics). It is also possible to virtually calculate a virtual value for the fractional flow reserve, a virtual FFR value, based on the three-dimensional model using a three-dimensional model of the vascular segment of the body that contains the stenosis. Further boundary conditions such as, for example, the blood flow in milliliters per second through the vascular segment of the body may also be calculated. Methods of this type are known and described, for example, in the article by Paul D. Morris et al.: ““Virtual” (Computed) Fractional Flow Reserve—Current Challenges and Limitations” in JACC: Cardiovascular Interventions, Vol. 8, No. 8, 2015, pages 1009 to 1117. Further calculation methods for a virtual FFR value are also known.
The approaches to virtual calculation of the fractional flow reserve may be divided into two groups: Non-invasive methods, in which geometric information relating to the vascular segment or vessel of the body is obtained by computed tomography, magnetic resonance tomography, or other methods; and minimally invasive methods, in which the geometric information is obtained with a subsequent x-ray recording in the heart catheter laboratory by injecting contrast agent into the vessel. A non-invasive examination is firstly carried out on a patient using computed tomography (CT). Aside from the diagnostic information relating to one or a number of vascular cross-sections of the examined vascular segment or vessel of the body, in such cases, a virtual value may also be calculated for the fractional flow reserve (e.g., CT-FFR value). In contrast, a virtual value for a fractional flow reserve, which is determined by angiography in the heart catheter laboratory, for example, is referred to below as angio-FFR value.
The CT-FFR method (e.g., the calculation of the virtual FFR value using a CT) is advantageous in that a three-dimensional model of the entire vascular tree, in which the vessel of the body or the vascular segment of the body with the stenosis is located, is available. The CT-FFR method also permits a good determination of the perfused myocardial mass and of the perfusion flow derived from the portion of the perfused myocardial mass. Additional information such as, for example, a combining of the stenosis or plaque may also be determined. The disadvantage is the comparably minimal spatial resolution and thus an inaccurate geometrical representation of the stenosis geometry.
By comparison, the angio-FFR method (e.g., the calculation of a virtual FFR value via an angiography) has the advantage of a good spatial resolution that allows for an accurate representation of the stenosis geometry. The disadvantage is the estimation of the blood through the vascular cross-sections. Small errors may already have significant repercussions. Estimating the blood flow via the contrast agent dynamics with the angio-FFR method is also complicated and difficult. It is also disadvantageous that the angio-FFR method provides no information relating to a state of the myocardial mass, which is important, for example, in order to identify possible initial damages so as to be able to take these into account during a treatment, for example. Geometric information of the entire vascular tree may only be achieved with extreme difficulty; this also relates back to the relatively small detectors that are typically used in angiographies.
To calculate an FFR value with the angio-FFR method, a segmentation of the two-dimensional recordings or angiography images and subsequently typically a generation of a three-dimensional angiography including at least two two-dimensional recordings may be provided. A recording or x-ray recording is also described here as an acquisition or angiography scene. The data contained in a recording may represent a film with a plurality of individual images at a generally fixed or non-variable predetermined angulation (e.g., a predetermined recording angle that is non-variable relative to the recorded vessel of the body for the acquisition or recording). In particular acquisitions, the individual images contained in a recording may be recorded at different angulations. In this case, the precise assignment of the individual images with the corresponding angulation is, however, required or provided.
A segmentation of the relevant vessel of the body into the at least two two-dimensional recordings is provided in order to generate a three-dimensional angiography.
This may take place automatically; however, this is very difficult to implement in the angiography recordings or angiography images that are typically achieved. This is because even when the corresponding recording angle is chosen carefully, one or a number of superimpositions of coronary blood vessels or vessels of the body that are filled with contrast agent are present one below the other or of other objects or vessels of the body (e.g., of catheters and further anatomical structures with the vascular segment of the body to be examined). Since the angiography images are often low-contrast, image noise also plays an important role here.
On account of patient movements such as, for example, the breathing or a movement of a patient couch of a corresponding x-ray device, the at least two projection recordings or angiographic recordings, which are to be provided for the three-dimensional angiography, do not always belong spatially together and are to be adjusted or corrected accordingly (e.g., movement-corrected). This typically takes place via a shared reference point that is automatically offered in a software such as “IZ3D” by Siemens, for example, and is insensitive to distortions or vascular deformations between the two angiographic recordings of the vessel of the body. In such cases, the shared reference point may be adjusted manually.